I. Field of the Invention
The present invention relates to separation of hydrocarbon and other catalysts and sorbents by magnetic separation, generally classified in Class 55; Subclass 3; and Class 120, Subclasses 119+ of the U.S. Patent and Trademark Office.
In fluid bed cracking of hydrocarbon feedstocks, it is the practice, because of the rapid loss in catalyst activity and selectivity, to continuously add fresh catalyst regularly, usually daily, to an equilibrium mixture of catalyst particles. These small microspherical particles vary in size from 10 to 150 microns and represent a highly dispersed mixture of catalyst particles. Some have been present in the unit for as little as one day, while others have been there for as long as 60-90 days or more. Because these particles are so small, no process has been available to remove old catalysts from new, therefore, it usually is customary to withdraw 1 to 10% or more of equilibrium catalyst which contains all of these variously aged particles just prior to addition of fresh catalyst particles, thus providing room for the incoming fresh material. Unfortunately, the 1 to 10% of equilibrium catalyst withdrawn contains 1-10% of the very expensive catalyst added the day before, 1-10% of the catalyst added 2 days ago, 1-10% of the catalyst added 3 days ago, and so forth. Therefore unfortunately, a large proportion of withdrawn catalyst represents still very active catalyst.
Consumption of particulate (which in preferred cases is cracking catalyst) can be very high. The cost associated therewith, especially when high nickel and vanadium are present in amounts greater than 0.1 ppm in the feedstock can, therefore, be very great. Depending on the level of metal content in feed and desired catalyst activity, tons of catalyst must be added daily. For example, the cost of a catalyst at the point of introduction to the unit can rise as high as $2,000/ton. As a result, a unit consuming 20 tons/day of catalyst would require expenditures each day of at least $40,000. For a unit processing 40,000 barrels per day this would represent a processing cost of $1/barrel or 2.5 cents/gallon, for catalyst use alone.
In addition to catalyst costs, an aged and highly nickel and vanadium laden catalyst can also bring about a reduction in yield of valuable and preferred liquid fuel products, such as gasoline and diesel fuel, and instead, produce more undesirable, less valuable products, such as dry gas and coke. A high level of nickel and vanadium on catalyst can also accelerate catalyst deactivation, thus further reducing operating profits.
Because of this required daily addition of catalyst (or sorbent) particulates, there results immediate and complete mixing of these microspherical particulates both fresh in performance and low in contaminants (usually nickel, vanadium, iron, copper, and sodium) with other microspherical particulates high in these adverse elements and very low in activity and which particulates have been in the unit for varying times as long as 60-90 days or longer. These older catalysts have drastically dropped in performance while simultaneously accumulating these aforementioned deleterious metal contaminants which catalytically greatly accelerate production of hydrogen and coke as well as dry gas.
As a result, industry has long felt a need to have a means by which the older (earlier added) catalyst can be selectively removed without inclusion or entrainment of the newer (freshly added) catalyst in order to reduce catalyst addition rates while at the same time maintaining better activity, selectivity and unit performance. Because of the very small size of these particles, billions of particles are involved, and mechanical separation has not been feasible even if one could rapidly identify by some means, as for example, color, which particles are old, and which are new.
II. Description of the Prior Art
"Magnetic Methods For The Treatment of Materials" by J. Svovoda published by Elsevier Science Publishing Company, Inc., New York (ISBNO-44-42811-9) Volume 8) discloses both theoretical equations describing separation by means of magnetic forces with the corresponding types of equipment that may be so employed. Specific reference at pages 135-137 is made to cross-belt magnetic separators and pages 144-149 refer to belt magnetic separators involving a permanent magnet roll separator, as well as pages 161-197 which refer to high gradient magnetic separators, all of which are efficient in separating magnetic particles.
A manual search in the U.S. Patent Office, Class 55, subclass 3; Class 208, subclasses 52CT, 113, 119, 120, 121, 124, 137, 139, 140, 152, 251R, and 253; Class 209, subclasses 8, 38, 39, and 40; and Class 502, subclasses 5, 20, 21, 38, 515, 516, and 518 found principally the following references: